1. Field of the Invention
The present relates to an apparatus and method for measuring the amount of aerosol medication remaining in an aerosol medication inhaler canister and for estimating the number of charges remaining therein.
2. Description of the Prior Art
A significant number of human beings suffer from a bronchial condition known as asthma. Asthmatic persons suffer from a paroxysmal disorder of respiration and at times experience labored breathing and a feeling of constriction in the chest. This condition is caused by an inflammation of bronchial tissues which constricts the air passageways in and to the lungs.
To provide temporary relief for an asthmatic condition, medication must be applied promptly. Such medication has for many years been provided through an inhaler which receives a measured charge of the medication from a canister and atomizes the medicinal charge as it is orally inhaled so that the medication is immediately applied to the inflamed tissues. The metered charges of medication are received through a mouthpiece coupled to a hollow metal or plastic canister which contains the medication. Such canisters are sold as prescription items and typically contain about 200 metered charges.
While asthma medication applied through an inhaler does provide the necessary temporary relief for a patient, long standing defects have existed in the container system for asthma medication. Specifically, a patient really has no means for determining how much medication is left in an aerosol medication inhaler canister. Since the canister contains numerous charges, it is impractical for a patient to attempt to keep track of the number of charges that have already been utilized from a canister. Furthermore, the exact number of charges in a canister will vary in any event.
As a consequence, a patient heretofore has had no systematic way of determining when the medication contents of an aerosol medication inhaler canister are nearly depleted, or indeed already have been depleted. Indeed, a patient is often only alerted to the fact that a canister is empty when utilization of it fails to provide relief from an asthma attack. Unless the patient has a refill canister readily available, the patient can be exposed to a very dangerous condition, and in any event is likely to experience considerable discomfort until a replacement canister has been fitted onto the inhaler mouthpiece and a charge of medication has been elicited therefrom.
To avoid becoming entrapped in a situation in which no medication is readily available, a patient is likely to discard and replace an aerosol medication canister prematurely when it is believed to be approaching a depleted condition, even though the original canister may contain a number of further metered charges. This is both wasteful and expensive, since refill cartridges are quite costly. Moreover, if a patient were aware of the approaching depletion of an aerosol medication canister, the patient would be in a position to purchase a replacement canister at the patient's convenience from a low cost or price discount source of supply, rather than being forced to spend a much larger amount in order to procure a refill canister under emergency conditions.
A further disadvantage of aerosol medication container systems is that sometimes the medication is depleted before the aerosol propellant. Under such circumstances a patient continues to activate the canister so as to deliver a charge of medication, but only receives a charge of the aerosol propellent. Thus, the patient is exposed to considerable discomfort until the patient realizes that the canister is no longer effective and that a replacement canister must be employed.
For some time it has been recognized that as inhaler canisters discharge their medication, the weight of the canister decreases. If a full canister is placed in a volume of water, it will sink to the bottom of the container. As the medication is depleted, the canister, if again placed in water, will tend to float at the surface of the water at an orientation corresponding to its state of depletion. Exemplary conditions of an aerosol medication canister in different states of depletion are illustrated at page 7 of the publication AIR CURRENTS, Volume 3, Number 2, March/April, 1992. However, heretofore there has been no system that allows a user to utilize this information in a systematic way so as to accurately measure the state of depletion of an aerosol medication canister.
Moreover, there are a considerable number of different models of canisters and a number of different manufacturers of aerosol medication canisters, each employing a canister of a slightly different configuration. As a consequence, the different models of canisters produced by various manufacturers will float at different orientations when empty. Therefore, there has heretofore been no universal system that allows a user to measure the state of depletion of different models of canisters utilizing a uniform procedure.